Internet-Draft TTL mapping for EPP August 2023
Brown Expires 2 February 2024 [Page]
Workgroup:
Registration Protocols Extensions (regext)
Internet-Draft:
draft-ietf-regext-epp-ttl-01
Published:
Intended Status:
Standards Track
Expires:
Author:
G. Brown
CentralNic Group plc

Extensible Provisioning Protocol (EPP) mapping for DNS Time-To-Live (TTL) values

Abstract

This document describes an extension to the Extensible Provisioning Protocol (EPP) that allows EPP clients to manage the Time-To-Live (TTL) value for domain name delegation records.

About this draft

This note is to be removed before publishing as an RFC.

The source for this draft, and an issue tracker, may can be found at https://github.com/gbxyz/epp-ttl-extension.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 2 February 2024.

Table of Contents

1. Introduction

The principal output of any domain name provisioning system is a DNS zone file, which contains the delegation record(s) for names registered within a zone (such as a top-level domain). These records include, at minimum, one or more NS records, but may also include A and/or AAAA glue records, DS records, and DNAME records for IDN variants ([RFC6927]).

Typically, the Time-To-Live value (TTL, see Section 5 of [RFC8499]) of these records is determined by the registry operator. However, in some circumstances it may be desirable to allow the sponsoring client of a domain name to change the TTL used for that domain: for example, to reduce the amount of time required to complete a change of DNS servers, DNSSEC deployment or key rollover, or to allow for fast rollback of such changes.

This document describes an EPP extension to the domain name and host object mappings (described in [RFC5731] and [RFC5732], respectively) which allows the sponsor of a domain name or host object to change the TTL associated with that object. It also describes how EPP servers should handle TTLs specified by EPP clients, and how both parties co-ordinate to manage TTL values in response to changes in operational or security requirements.

1.1. Conventions used in this document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

In examples, "C:" represents lines sent by a protocol client and "S:" represents lines returned by a protocol server. Indentation and white space in examples are provided only to illustrate element relationships and are not REQUIRED features of this protocol.

A protocol client that is authorized to manage an existing object is described as a "sponsoring" client throughout this document.

XML is case sensitive. Unless stated otherwise, XML specifications and examples provided in this document MUST be interpreted in the character case presented in order to develop a conforming implementation.

EPP uses XML namespaces to provide an extensible object management framework and to identify schemas required for XML instance parsing and validation. These namespaces and schema definitions are used to identify both the base protocol schema and the schemas for managed objects.

The XML namespace prefixes used in examples (such as the string ttl in ttl:secs) are solely for illustrative purposes. A conforming implementation MUST NOT require the use of these or any other specific namespace prefixes.

2. Extension elements

This specification defines a new element, <ttl:secs>, that is included in <info> responses, and <create> and <update> commands.

The <ttl:secs> element takes two forms. The first contains a 32-bit unsigned integer indicating the TTL (expressed in seconds) which will be applied to the DNS records for the associated domain name or host object.

Example:

<ttl:secs>3600</secs>

The second form, which contains no content, indicates that (a) in <info> responses, no specific value has been set for the object, or (b) in <create> and <update> commands, that the client wishes to remove a previously set value, in favour of the default value. Note that this does no mean that no TTL is published in DNS records (since this is not possible), rather, that the server-determined default TTL is (or should be) used for that object.

Example:

<ttl:secs/>

3. EPP command mapping

3.1. EPP query commands

3.1.1. EPP <info> command

This extension defines an additional element for EPP <info> responses for domain and host objects.

When a server receives a domain or host <info> command from a client which included the extension namespace in the <svcExtension> element of the <login> command, the response MUST contain an <extension> element, which MUST contain a <ttl:infData> element. This element contains a single <ttl:secs> element.

Example domain <info> response:

S: <?xml version="1.0" encoding="utf-8" standalone="no"?>
S: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
S:   <response>
S:     <result code="1000">
S:       <msg>Command completed successfully</msg>
S:     </result>
S:     <resData>
S:       <domain:infData
S:         xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
S:         <domain:name>example.com</domain:name>
S:         <domain:roid>EXAMPLE1-REP</domain:roid>
S:         <domain:status s="ok" />
S:         <domain:registrant>jd1234</domain:registrant>
S:         <domain:contact type="admin">sh8013</domain:contact>
S:         <domain:contact type="tech">sh8013</domain:contact>
S:         <domain:ns>
S:           <domain:hostObj>ns1.example.com</domain:hostObj>
S:           <domain:hostObj>ns1.example.net</domain:hostObj>
S:         </domain:ns>
S:         <domain:clID>ClientX</domain:clID>
S:         <domain:crID>ClientY</domain:crID>
S:         <domain:crDate>1999-04-03T22:00:00.0Z</domain:crDate>
S:         <domain:upID>ClientX</domain:upID>
S:         <domain:upDate>1999-12-03T09:00:00.0Z</domain:upDate>
S:         <domain:exDate>2005-04-03T22:00:00.0Z</domain:exDate>
S:         <domain:trDate>2000-04-08T09:00:00.0Z</domain:trDate>
S:         <domain:authInfo>
S:           <domain:pw>2fooBAR</domain:pw>
S:         </domain:authInfo>
S:       </domain:infData>
S:     </resData>
S:     <extension>
S:       <ttl:infData
S:         xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0">
S:         <ttl:secs>3600</ttl:secs>
S:       </ttl:infData>
S:     </extension>
S:     <trID>
S:       <clTRID>ABC-12345</clTRID>
S:       <svTRID>54322-XYZ</svTRID>
S:     </trID>
S:   </response>
S: </epp>

Example host <info> response:

S:<?xml version="1.0" encoding="UTF-8" standalone="no"?>
S: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
S:   <response>
S:     <result code="1000">
S:       <msg>Command completed successfully</msg>
S:     </result>
S:     <resData>
S:       <host:infData
S:        xmlns:host="urn:ietf:params:xml:ns:host-1.0">
S:         <host:name>ns1.example.com</host:name>
S:         <host:roid>NS1_EXAMPLE1-REP</host:roid>
S:         <host:status s="linked"/>
S:         <host:status s="clientUpdateProhibited"/>
S:         <host:addr ip="v4">192.0.2.2</host:addr>
S:         <host:addr ip="v4">192.0.2.29</host:addr>
S:         <host:addr ip="v6">1080::8:800:200C:417A</host:addr>
S:         <host:clID>ClientY</host:clID>
S:         <host:crID>ClientX</host:crID>
S:         <host:crDate>1999-04-03T22:00:00.0Z</host:crDate>
S:         <host:upID>ClientX</host:upID>
S:         <host:upDate>1999-12-03T09:00:00.0Z</host:upDate>
S:         <host:trDate>2000-04-08T09:00:00.0Z</host:trDate>
S:       </host:infData>
S:     </resData>
S:      <extension>
S:        <ttl:infData
S:          xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0">
S:          <ttl:secs>3600</ttl:secs>
S:        </ttl:infData>
S:      </extension>
S:     <trID>
S:       <clTRID>ABC-12345</clTRID>
S:       <svTRID>54322-XYZ</svTRID>
S:     </trID>
S:   </response>
S: </epp>

3.2. EPP transform commands

3.2.1. EPP <create> command

This extension defines an additional element for EPP <create> commands for domain and host objects.

The <create> command MAY contain an <extension> element which MAY contain a <ttl:create> element. This element contains a single <ttl:secs> element.

Example domain <create> command:

C: <?xml version="1.0" encoding="UTF-8" standalone="no"?>
C: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
C:   <command>
C:     <create>
C:       <domain:create
C:        xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
C:         <domain:name>example.com</domain:name>
C:         <domain:period unit="y">2</domain:period>
C:         <domain:ns>
C:           <domain:hostObj>ns1.example.net</domain:hostObj>
C:           <domain:hostObj>ns2.example.net</domain:hostObj>
C:         </domain:ns>
C:         <domain:registrant>jd1234</domain:registrant>
C:         <domain:contact type="admin">sh8013</domain:contact>
C:         <domain:contact type="tech">sh8013</domain:contact>
C:         <domain:authInfo>
C:           <domain:pw>2fooBAR</domain:pw>
C:         </domain:authInfo>
C:       </domain:create>
C:     </create>
C:     <extension>
C:       <ttl:create
C:         xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0">
C:         <ttl:secs>3600</ttl:secs>
C:       </ttl:create>
C:     </extension>
C:     <clTRID>ABC-12345</clTRID>
C:   </command>
C: </epp>

Example host <create> command:

C:<?xml version="1.0" encoding="UTF-8" standalone="no"?>
C: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
C:   <command>
C:     <create>
C:       <host:create
C:        xmlns:host="urn:ietf:params:xml:ns:host-1.0">
C:         <host:name>ns1.example.com</host:name>
C:         <host:addr ip="v4">192.0.2.2</host:addr>
C:         <host:addr ip="v4">192.0.2.29</host:addr>
C:         <host:addr ip="v6">1080::8:800:200C:417A</host:addr>
C:       </host:create>
C:     </create>
C:     <extension>
C:       <ttl:create
C:         xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0">
C:         <ttl:secs>3600</ttl:secs>
C:       </ttl:create>
C:     </extension>
C:     <clTRID>ABC-12345</clTRID>
C:   </command>
C: </epp>

If an EPP server receives a <create> command containing a TTL that is outside the server's permitted range, it MUST reject the command with a 2306 "Parameter value policy error" response.

3.2.2. EPP <update> command

This extension defines an additional element for EPP <update> commands for domain and host objects.

The <update> command MAY contain an <extension> element which MAY contain a <ttl:update> element. This element contains a single <ttl:secs> element.

Example domain <update> command:

C: <?xml version="1.0" encoding="UTF-8" standalone="no"?>
C: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0"
C:      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
C:   <command>
C:     <update>
C:       <domain:update
C:        xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
C:         <domain:name>example.com</domain:name>
C:       </domain:update>
C:     </update>
C:     <extension>
C:        <ttl:update>
C:          xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0">
C:          <ttl:secs>3600</ttl:secs>
C:        </ttl:update>
C:      </extension>
C:     <clTRID>ABC-12345</clTRID>
C:   </command>
C: </epp>

Example host <update> command:

C:<?xml version="1.0" encoding="UTF-8" standalone="no"?>
C: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
C:   <command>
C:     <update>
C:       <host:update
C:        xmlns:host="urn:ietf:params:xml:ns:host-1.0">
C:         <host:name>ns1.example.com</host:name>
C:         <host:add>
C:           <host:addr ip="v4">192.0.2.22</host:addr>
C:           <host:status s="clientUpdateProhibited"/>
C:         </host:add>
C:         <host:rem>
C:           <host:addr ip="v6">1080::8:800:200C:417A</host:addr>
C:         </host:rem>
C:         <host:chg>
C:           <host:name>ns2.example.com</host:name>
C:         </host:chg>
C:       </host:update>
C:     </update>
C:     <extension>
C:        <ttl:update>
C:          xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0">
C:          <ttl:secs>3600</ttl:secs>
C:        </ttl:update>
C:      </extension>
C:     <clTRID>ABC-12345</clTRID>
C:   </command>
C: </epp>

If an EPP server receives an <update> command containing a TTL that is outside the server's permitted range, it MUST reject the command with a 2306 "Parameter value policy error" response.

4. Server processing of TTL values

4.1. Use of TTL values in delegation records

EPP servers which implement this extension SHOULD use the values provided by EPP clients for the TTL values of NS and DS records published in the DNS for domain objects, and A and AAAA records published in the DNS for host objects.

EPP servers that use the "host attribute" model (described in section 1.1 of [RFC5731]) SHOULD use the TTL of the domain object when publishing NS, A and AAAA records derived from host attributes.

4.2. Relationship between host object and domain object TTL values

The extension in this document allows TTL values to be configured for both domain and host objects. In domain name registries, these object types have a hierarchical relationship, in that a host object may be subordinate to a domain object: for example, the host object ns1.example.com is subordinate to the domain object example.com.

When publishing A and AAAA for host objects, TTL values for host objects SHOULD take precedence over the TTL of the superordinate domain object. However, if no TTL value is specified for a subordinate host object, but a TTL value is specified for the superordinate domain object, then the domain object's TTL value MAY be used for the host object instead of the default TTL value.

4.3. Use of TTL values for IDN variants

If a domain name has variants ([RFC6927]) that are linked to that domain, then any NS or DNAME records published for those variants MAY use the same TTL as that used for the primary domain.

5. Out-of-band changes to TTL values

EPP server operators MAY, in order to address operational or security issues, make changes to TTL values out-of-band (that is, not in response to an <update> command received from the sponsoring client).

Additionally, server operators MAY implement an automatic reset of TTL values, so that they may be changed for a finite period before and after a planned change, and then revert to a standard value.

If a TTL value is changed out-of-band, EPP server operators MAY notify the sponsoring client using the EPP Change Poll extension ([RFC8590]), which provides a generalised method for EPP servrers to notify clients of changes to objects under their sponsorship.

6. Operational considerations

6.1. Operational impact of TTL values

Domain registry operators must strike a balance between, on the one hand, the desire of registrants for changes to their domains to be visible in the DNS quickly, and on the other, the increased DNS query traffic that short TTLs can bring. Historically, registry operators have used a global TTL value which was applied to all delegations within their zones, which could then be tuned to an optimum value.

Domain registry operators SHOULD implement limits on the maximum and minimum accepted TTL values that are narrower than the values permitted in the XML schema in the Formal syntax (which were chosen to allow any TTL permitted in DNS records), in order to prevent scenarios where an excessively high or low TTL causes operational issues on either side of the zone cut.

Section 5 describes how server operators MAY unilaterally change TTL values in order to address operational or security issues, or only permit changes for limited time periods (after which TTLs revert to the default).

6.2. When the TTL should be changed

A common operational mistake is changing of DNS record TTLs during or after the planned change to the records themselves. This arises due to a misunderstanding about how TTLs work.

Client implementations of this specification SHOULD ensure that the user understands that changes to a TTL are only effective in shortening transition periods if implemented a period of time — at least equal to the current TTL — before the planned change.

7. Security considerations

Some malicious actors use a technique called "fast flux DNS" ([SAC-025]) to rapidly change the DNS configuration for a zone in order to evade takedown and law enforcement activity.

Registry operators SHOULD take this into consideration when setting the lower limit on TTL values, since a short TTL on delegations has the potential to enhance the effectiveness of fast flux techniques on evasion.

8. IANA considerations

8.1. XML namespace

This document uses URNs to describe XML namespaces and XML schemas conforming to a registry mechanism described in [RFC3688]. The following URI assignment has been made by IANA:

Registration for the TTL namespace:

  • URI: urn:ietf:params:xml:ns:epp:ttl-1.0
  • Registrant Contact: See the author of this document
  • XML: None. Namespace URIs do not represent an XML specification

Registration for the TTL XML schema:

  • URI: urn:ietf:params:xml:schema:epp:ttl-1.0
  • Registrant Contact: See the author of this document
  • XML: See the "Formal syntax" section of this document

8.2. EPP extension registry

The EPP extension described in this document has been registered by the IANA in the Extensions for the "Extensible Provisioning Protocol (EPP)" registry described in [RFC7451]. The details of the registration are as follows:

  • Name of Extension: Extensible Provisioning Protocol (EPP) Mapping for DNS Time-To-Live (TTL) values
  • Document Status: Standards Track
  • Reference: URL of this document
  • Registrant Name and Email Address: See the author of this document
  • TLDs: Any
  • IPR Disclosure: None
  • Status: Active
  • Notes: None

9. Formal syntax

The formal syntax presented here is a complete schema representation of the extension suitable for automated validation of EPP XML instances.

<?xml version="1.0" encoding="UTF-8"?>
<schema
  targetNamespace="urn:ietf:params:xml:ns:epp:ttl-1.0"
  xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0"
  xmlns="http://www.w3.org/2001/XMLSchema"
  elementFormDefault="qualified">
  <annotation>
    <documentation>
      Extensible Provisioning Protocol v1.0 extension schema for
      Time-To-Live (TTL) values for domain and host objects.
    </documentation>
  </annotation>

  <element name="create"  type="ttl:seconds"/>
  <element name="update"  type="ttl:seconds"/>
  <element name="infData" type="ttl:seconds"/>

  <complexType name="seconds">
    <choice>
      <element name="secs" type="ttl:nonNegativeInteger"/>
      <element name="secs"/>
    </choice>
  </complexType>

  <simpleType name="nonNegativeInteger">
    <restriction base="nonNegativeInteger">
      <minInclusive value="0"/>
      <maxInclusive value="2147483647"/>
    </restriction>
  </simpleType>
</schema>

10. Change Log

This section is to be removed before publishing as an RFC.

10.1. Change from 00 to 01

  1. Incorporate feedback from Jim Gould.
  2. Add wording to describe how TTL values are jointly managed by both clients and servers.
  3. Fix minimum/maximum TTL value and schema namespace (thanks Patrick Mevzek).
  4. Moved text on how the server should handle impermissible TTL values from the top of Section 4 to Sections 3.2.1 and 3.2.2 (thanks Rick Wilhelm).
  5. Namespace changed from urn:ietf:params:xml:ns:ttl-1.0 to urn:ietf:params:xml:ns:epp:ttl-1.0.
  6. Added discussion on EPP servers which use the host attribute model in Section 4.1 (thanks Hugo Salgado).
  7. Added a Change Log (Section 10).

11. References

11.1. Normative references

[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC3688]
Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, , <https://www.rfc-editor.org/info/rfc3688>.
[RFC5731]
Hollenbeck, S., "Extensible Provisioning Protocol (EPP) Domain Name Mapping", STD 69, RFC 5731, DOI 10.17487/RFC5731, , <https://www.rfc-editor.org/info/rfc5731>.
[RFC5732]
Hollenbeck, S., "Extensible Provisioning Protocol (EPP) Host Mapping", STD 69, RFC 5732, DOI 10.17487/RFC5732, , <https://www.rfc-editor.org/info/rfc5732>.
[RFC7451]
Hollenbeck, S., "Extension Registry for the Extensible Provisioning Protocol", RFC 7451, DOI 10.17487/RFC7451, , <https://www.rfc-editor.org/info/rfc7451>.
[RFC8499]
Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499, , <https://www.rfc-editor.org/info/rfc8499>.
[RFC8590]
Gould, J. and K. Feher, "Change Poll Extension for the Extensible Provisioning Protocol (EPP)", RFC 8590, DOI 10.17487/RFC8590, , <https://www.rfc-editor.org/info/rfc8590>.

11.2. Informative references

[RFC6927]
Levine, J. and P. Hoffman, "Variants in Second-Level Names Registered in Top-Level Domains", RFC 6927, DOI 10.17487/RFC6927, , <https://www.rfc-editor.org/info/rfc6927>.
[SAC-025]
ICANN Security and Stability Advisory Committee (SSAC), "SSAC Advisory on Fast Flux Hosting and DNS", SAC 25, , <https://www.icann.org/en/system/files/files/sac-025-en.pdf>.

Author's Address

Gavin Brown
CentralNic Group plc
44 Gutter Lane
London
EC2V 6BR
United Kingdom